The present application relates to a battery. In particular, the present application relates to a nonaqueous electrolyte secondary battery.
In recent years, downsizing and weight reduction of mobile information terminals such as mobile phones, laptop personal computers and PDA are rapidly developing, and batteries as a drive power source thereof are required to realize a higher capacity. Since nonaqueous electrolyte secondary batteries represented by lithium ion secondary batteries have a high energy density and a high capacity, they are widely utilized as a drive power source for the foregoing mobile information terminals. In particular, since laminated batteries using an aluminum laminated film for an exterior are lightweight, they have a large energy density. In laminated batteries, when an electrolytic solution is swollen into a polymer, deformation of the laminated battery can be suppressed, and therefore, laminated polymer batteries are also widely used.
In an electrode of such a battery, an active material bearing an oxidation-reduction reaction is in general carried on a collector by a binder. It is necessary to design the binder such that bonding to the collector as well as bonding to the active material is stably secured with time at use of the battery (see Japanese Patents Nos. 3,121,943, 3,661,945 and 3,999,927).
However, among up-to-date binders, there was included a system in which a cycle performance of the battery drops because separation between the binder and the active material or separation between the collector and the binder is caused due to expansion/contraction of the active material.
In lithium ion secondary batteries, especially under the cycle, the binder cannot follow the expansion/contraction of the active material, and adhesion between the collector and the active material layer is lowered. Therefore, there was involved such a problem that not only electrical conductivity is lowered, but a cycle performance is lowered.